Research On Integrated Control Strategy Of Electric Power Steering And Active Front Steering Based On The Kalman Filter

The steering system is the input device for the driver to direct manipulation and control the vehicle. Its function has important influence on the handing stability and safety of the vehicle. Electric power steering system(EPS) is from the point of power and provide appropriate steering power by the power actuator based on the information of vehicle speed and the steering wheel torque. It will make sure the driver's operation more convenient, comfortable and safe. Active front steering system(AFS) is from the point of the superposition angle and provide the superposition angle to the steering system based on the information of the speed and vehicle stability by angle assist actuator. It will good for the driver's operation and improve the stability and safety of vehicle. EPS and AFS are to improve vehicle performance from different points. Therefore, the integration of the two systems will greatly improve the performance of the steering system.Firstly, the vehicle model, tire model, electric power steering system model and active front steering system model are established and the simulation models are built in Matlab/simulink. The effectiveness of the simulation model is verified through the comparative analysis with carsim model.Secondly, the Kalman filtering theory is introduced in order to obtain the states and parameters of the vehicle used for the integrated control. The core formla of the Kalman filtering theory is derived from the point of mathematical analysis. The vehicle state observer is designed based on the Kalman filtering theory to estimate vehicle state. Because the tire force is a nonlinear function of the tire road friction coefficient, the observer of the tire road friction coefficient is designed based on the extended Kalman filter theory to estimate the tire road friction coefficient. The simulation results prove the accuracy and effectiveness of the estimation.Then, the controlled studies are designed for the electric power steering and active front steering subsystem respectively. The electric power steering control is designed based on tire force estimates using the Kalman observer. So the driver can obtain the same road feel as on the high adhesion road when the vehicle is on the low adhesion road. In order to provide the appropriate information of the road to the driver, the compensate correction is designed for the traditional electric power current using the fuzzy control rules based on the information of the estimate of the road adhesion and the speed. Sliding mode control is designed for the AFS controller of vehicle stability. Simulation results show the validity of the above controllers.Finally, the reasons of the system integrated are introduced and the interaction between EPS and AFS is analyzed. The power correction control considering road adhesion is designed based on the estimates of the tire force and road adhesion. It solves the interaction so that it can ensure the function of AFS and provide the appropriate road feel to the driver through EPS at the same time.